A typical distributed database system with a shared disk storage arrangement involves one or more servers correcting via communication network and cooperating with each other to manage a distributed database stored on a stable database storage. Additionally, the typical distributed database system must be capable of maintaining data consistency across all the servers. Users, on any server, may send queries to modify the distributed database. The typical distributed database system must be able to synchronize any modification originating from any server and present a consistent, view to all the servers. As a result, synchronization becomes a necessary function in maintaining data consistency.
Metadata are information about actual data in the distributed database which help the distributed database system find or access the actual data from the distributed database. Each server may read information from the stable database storage (shared persistent storage) and generate metadata for a particular database object. These metadata are typically stored privately on each server's memory and do not have a persistent copy on the shared persistent storage.
A user query that modifies the data can lead to modification of metadata as well. However, this process modifies the privately held copy of the metadata on the server on which the query was executed. Hence, in a typical shared disk distributed database system, it is necessary to synchronize this metadata information between all the servers so that all copies of the metadata stored locally at each server presents a consistent view of the database.
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